Re: [quicwg/base-drafts] Describe interaction between QUIC and TLS regarding saved 0-RTT state (#2947)

[Kazuho Oku <[e-mail]>]

kazuho commented on this pull request.

The text looks like a nice improvement :+1: :+1:. LGTM modulo the point below.

> @@ -644,6 +647,27 @@ A client MAY attempt to send 0-RTT again if it receives a Retry or Version
 Negotiation packet.  These packets do not signify rejection of 0-RTT.
 
 
+## Validating 0-RTT Configuration
+
+When a server receives a ClientHello with the "early_data" extension, it has to
+decide whether to accept or reject early data from the client. Some of this
+decision is made by the TLS stack (e.g., checking that the cipher suite being
+resumed was included in the ClientHello; see Section 4.2.10 of {{!TLS13}}). Even
+when the TLS stack has no reason to reject early data, the QUIC stack or the
+application protocol using QUIC might reject early data because the
+configuration of the transport or application associated with the resumed
+session is not compatible with the server's current configuration.
+
+QUIC requires additional transport state to be associated with a 0-RTT session
+ticket. If stateless session tickets are used, this information must be stored
+in the session ticket. Application protocols that use QUIC might have similar

While it is true that additional transport state needs to be associated and verified when doing 0-RTT resumption, I am not sure if that necessarily mean that "this information must be stored in the session ticket."

For example, a server might store the associated states in a NEW_TOKEN token, that also contains the hash value of the session ticket. In such a design, when accepting a new connection, a server can consult the pair of the token and the session ticket, and decide if it can accept 0-RTT.

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